I have used CO2 in a discus tank, but only sparingly, with a low bubble count, and kept a careful eye on it.
But with discus, I've found that the best, most successful approach is to keep things as simple as possible.
So in keeping with that, almost all of my discus tanks (over nearly 40 years of keeping discus, on & off) have been low tech, with the occasional use of Excel and liquid or dry macro & micro ferts, but with the emphasis placed mainly on using root tab ferts in pool filter sand to grow the rooted plants. I use fairly low density lighting (discus don't seem to care for high lighting anyway), for limited daily time periods of approx. 7 hrs./day, and with overall plantings being on the light side, so algae has seldom been a problem.
As to raising fry, answering your question is a touch difficult, as it obviously depends so very much on how many fry you have at a given time, and what size they are at various stages in their growth.
You can keep a reasonable amount of fry in a 10 gal tank once they have been weaned from the parents, and are around dime-sized. But if they are well fed multiple daily times, and the tank is bare-bottom, with large daily wcs, they'll grow very quickly, up to an inch per month - so you can imagine how quickly they'll need a 20 gal; then a 40 gal say, soon following that.
8 week old discus can very well be near/around the 2" size, but their growth will likely slow perceptibly when they approach 3". After that the growth might be 3/4" or less per month, for the ensuing 2-4 months.
Most hobbyist discus breeders place their young for sale around the 2" or so size (generally, no larger, and no smaller), which usually takes 8-10 weeks or so. At that stage, their immune systems are still not well developed, and it takes several more months of multiple feedings and large daily wcs to grow them out properly into well-shaped fish that have the potential to reach a decent adult size (around 6" or more). Lots of work - good reason why the price of discus @ 2" doubles or triples in amount when they reach juvenile size of 3" to 4" or so.
Hope this helps inform you.
I'd like to provide a photo of one of my tanks to illustrate the manner in which I set them up and simplify, but all my pics are albumed in photobucket.com, whose web site happens to be down temporarily for maintenance just now, but I'll post a photo a bit later.
Here's the photo I promised:
It's a 75 gal tank with 3"-3.5" juvenile red snake skin discus.
Why am I risking growing out young juvenile discus in a planted tank vs. bare-bottom, you ask ?
1. - Because I have quite a few years' experience raising discus in planted tanks, and I don't neglect doing large, frequent wcs.
2. - I spend a lot of time keeping the tank squeaky clean - so water quality & conditions are pretty much ideal at all times.